Electrophotographic photoconductive layer comprising an organic photoconductor and a dicyanomethylene-indenothiophene sensitizer

ABSTRACT

Electrophotographic light-sensitive materials having a photoconductive layer formed on an electroconductive support, the photoconductive layer comprising an organic photoconductive compound (monomer or polymer) and 4-dicyanomethylene-4Hindeno(1,2-b)thiophene or 8-dicyanomethylene-8H-indeno(2,1b)thiophene or their derivatives as sensitizers, and processes for preparing such compounds from 4H-indeno(1,2-b)thiophene-4-one or 8H-indeno(2,1-b)thiophen-8-one or their derivatives and malonitrile.

United States Patent 1191 Hashimoto [75] Inventor: Mitsuru Hashimoto,Tokyo, Japan [73] Assignee: Kabushiki Kaisha Ricoh, Tokyo,

Japan 22 Filed: Dec. 19, 1973 21 Appl. No.: 425,967

[30] Foreign Application Priority Data Dec 28, 1972 Japan 48-1944 Dec.28, 1972 Japan 48-1945 [52] US. Cl. 96/l.5, 96/1.6, 260/329 F,

260/3322 R [51] Int. Cl G03g 5/06 [58} Field of Search 9 6/I.5, 1.6

l 56] References Cited UNITED STATES PATENTS 2,980,535 4/1961.Schroeter. ..l 96/1.5 X 3,244,516 4/1966, Neugebauer ct 3,252,794 5/1966Schnum ct a1. 96/15 3,301,676 l/1967 Tomanek 96/].5 3,307,940 3/1967Shattuck et a1 96/1.5 3.485625 12/1969 Fox 96/l.5

[451 Mar. 18, 1975 3,583,869 6/1971 Tubuko 96/15 3,677,752 7/1972 Lookeret al. 96/l.5 X 3,752,668 8/1973 Baltazzi 96/15 3,764,317 10/1973Depoorter et a1. 96/].6 X 3,765,882 10/1973 3,796,572 3/1974 Hashimoto96/1.5

OTHER PUBLICATIONS Wagner et al., A Study of the Relation of ElectronAffinity to the Photoconductivity of Doped PolyN-Vinylcarbazole Films: ANew Method of Analyzing the Photoresponse, Photographic Science and,

Engineering, Vol. 14, No. 3, May-June, 1970, pp.

Primary E.\-aminerNorman G. Torchin Assistant Examiner-John R. MillerAttorney, Agent, or FirmCooper, Dunham, Clark, Griffin & Moran [57]ABSTRACT Electrophotographic light-sensitive materials having aphotoconductive layer formed on an electroconductive support, thephotoconductive layer comprising an organic photoconductive compound(monomer or polymer) and 4-dicyanomethylene-4H-indeno[1,2- blthiopheneor 8-dicyanomethylene-8H-indeno[2,1- blthiophene or their derivatives assensitizers, and processes for preparing such compounds from 4H-indeno[1,2-b1thiophene-4-0ne or 8H-indeno[2,lblthiophen-v8-one or theirderivatives and malonitrile.

5 Claims, No Drawings 1 ELECTROPIIOTOGRAPHIC PHOTOCONDUCTIVE LAYERCOMPRISING AN ORGANIC PHOTOCONDUCTOR AND ADICYANOMETHYLENE-INDENOTHIOPHENE SENSITIZER RELATED APPLlCATION US. Pat.application Ser. No. 416,792, filed Nov. 19, 1973, describes and claimsthe corresponding indenothiophenones which are starting materials forthe compounds of this invention.

BACKGROUND OF THE INVENTION:

Electrophotographic light-sensitive materials comprise anelectroconductive support with a photocon-.

ductive layer formed thereon. The principle of an electrophotographicprocess is that an electrostatic latent image is produced by image-wiseexposure of a charged photoconductive layer and the image is thendeveloped by a developer or toner (in liquid or powder form) which iselectrically precipitated on the latent image to form a visible image.conventionally, for forming the photoconductive layer, inorganicphotoconductors such as photoconductive zinc oxide or selenium are used.Recently, the use of an organic photoconductive compound, e.g., a photoconductive polymer such as poly-N-vinylcarbazole in place of theinorganic photoconductors has been proposed. Amongst the advantages oforganic photoconductive compounds are transparency and mechanicalflexibility. Additionally, they are easy to form into photoconductivelayers. On the other hand, they absorb light in the ultraviolet regionof the spectrum, but are not sensitive to visible light. To overcomethis disadvantage, i.e., to shift their absorption into the visibleregion of the spectrum, dyestuff sensitizers are added to the organicphotoconductive compounds. Such dyestuffs as have been previouslyemployed are generally not stable and bleach out quickly so that theorganic photoconductive compounds lose their sensitivity in the visibleregion. As a result, electrophotographic light-sensitive materialsprepared utilizing organic photoconductive compounds containing dyestuffsensitizers are of limited practical use.

It is, therefore, an object of the present invention to provide stablesensitizers and improved electrophotographic light-sensitive materialscontaining such stable sensitizers.

SUMMARY OF THE INVENTION The present invention relates toelectrophotographic light-sensitive materials having a photoconductivelayer formed on an electroconductive support, the photoconductive layercomprising an organic photoconductive compound such as a photoconductivemonomer or polymer and 4-dicyanomethylene-4H- indcnol l.2-b}thiophene orS-diCyanomethyIene-SH- indcnol 2,l-h Ithiophcne or their derivatives asa sensitixcr. and a process or preparing such compounds and theirderivatives.

In general, electrophotographic light-sensitive matcriuls comprise anelectroconductive support and a photoconductive layer formed on thesupport.

The electrophotographic light-sensitive materials of the presentinvention are characterized in that the photoconductive layer comprisesan organic photoconductive compound sensitized with4-dicyanomethylenesuch 2 4l-l-indeno[l,2-b]thiophene or8-dicyanomethylene- 8l-l-indeno[2,l-b]thiophene and their derivativeshaving the following general formulas. These compounds are used assensitizers for the organic photoconductive compound.

I Ru

S H 3 t -qlr...

wherein R R R R R and R are hydrogen or nitro groups.

7 These compounds are respectively designated as follows:

A. 8-dicyanomethylene-8H-indeno[2,l-b]thiophene. B.4-dicyanomethylene-4H-indeno[ l ,2-b]thiophene. The electrophotographiclight-sensitive materials of the present invention may be prepared byforming a photoconductive layer on an electroconductive support, thephotoconductive layer comprising any of a variety or organicphotoconductive monomers such as N- vinylcarbazole or organicphotoconductive polymers as poly-N-vinylcarbazole and 4-dicyanomethylene-4H-indeno[1,2-b]thiophene or 8-dicyanomethylene-8H-indeno[2, l -b]thiophene or their derivatives asindicated above. 4-decyanomethylene- 4H-indeno[l,2-b]thiophene or8-dicyanomethylene 8H-indeno[2,l-b]thiophene or their derivatives areutilized in an amount of from 0.01 to 1.2 mole per mole of organicphotoconductive monomer or per monomeric unit of the organicphotoconductive polymer (1 mole of the organic photoconductive polymeris represented by monomeric unit of the polymer).

4-dicyanomethylene-4H-indeno[1,2-b1thiophene or8-dicyanomethylene-8I-I-indeno[2,1-b]thiophene and its derivatives foruse in accordance with the present invention are shown by structuralformulas below:

3 2-nitro-4-dicyanomethylene-4H-indeno[ 1,2-

blthiophene 6-nitro-4-dicyanomethylene-4H-indeno[1,2-

b]thiophene 2,6-dinitro-4-dicyanomethylene-4H-indeno[1,2-

b]thiophene v O N NC'CCN 6,8-dinitro-4-dicyanomethylene-4H-indeno[1,2-

b]thiophene NC'CCN 2,6,8-trinitro-4-dicyanomethylene-4H-indeno[1,2-

b]th|ophene 5O NC'C'CN (VII)8-dicyanomethylene-8H-indeno-[2,l-b]thiophene 4C C CN2-nitro-8-dicyanomethylene-8H-indeno-[2, l-

b]thi'ophene 6 -nitro-8-dicyanomethylene-8H-indeno-[2, l

blthiophene NC-C'CN OgN 2,6-dinitro-8-dicyanomethylene-8H-indeno-[ 2, l

b]thiophene 4,6-dinitro-8-dicyanomethylene-8 H-indeno-[2, l

b ]thiophene NC "C "CH 2,4,6-trinitro-8-dicyanomethylene-8H-indeno-[ 2,l

b]thiophene Organic photoconductive compounds for use in accordance withthe present invention include the followmg:

Preferred organic photoconductive polymers includepoly-N-vinylcarbazole, chlorinated or brominated poly-N-vinylcarbazole,polyvinylpyrene, polyvinylnaphthalene, polyvinylanthracene, poly-9-vinylfluorene, poly-l-arylimidazole, bromopyreneformaldehyde resin andpoly-p-phenylene-l ,3 ,4- oxadiazole.

Electrophotographic light-sensitive materials in accordance with thepresent invention can be produced, for example, as follows:

From about 0.01 to about 1 mole .of 4-dicyanomethylene-4H-indeno[l,2b]thiophene or 8-dicyanomethylene-8H-indeno[2,l-b]thiophene or their derivatives as shownabove is mixed with 1 mole of the organic monomer or monomeric unit ofthe organic photoconductive polymer and the'mixture is dissolvedobtained was evaluated using Electrostatic paper analyser Type SP-428sold by kawaguchi Denki Seisakusho as follows:

The material obtained above was divided into two 5 parts. Thephotoconductive layer was negatively or positively charged by a coronadischarge of about 6kV or +6kV for 20 seconds to obtain a surfaceelectric potential Vdo and then subjected to dark decay for 20 secondsto obtain a surface residual potential Vpo.

in an organic solvent such as tetrahydrofuran or dioxl0 T glight-Sensitive i l exposed to a ane to prepare a light-sensitivesolution. Polyester tungsten fllafnent Whose 1lll1mma ne at the resin,novolac resin or acrylic resin may, if desired, be faee of ehght'sensltlve layer was adlusted to be 20 added to this solution.Furthermore, polychlorobiphe; T (Seconds) required t0 reduce the f finyl may be added to this Solution The resulting gh electric potential toone half or one fifth of the residual sensitive solution is then appliedto a surface of an'elec- 15 Surface Potentlal P were measured- Theameems of troconductive support. for example, using a doctor exposure, 12 (lux'sec) and E (lux-sec),requ1red to blade, left to Set andflwndriedv reduce the surface electric potential to one half and Thefollowing Examples are given by way of illustraone fifth of P arecalculated by lux Xfl ction only. onds). The E and E represent thesensitivity of the 2O electrophotographic light-sensitive material. Thelower h EXAMPLE 1 the value of E 'or E the higher the sensitivity of theA light-sensitive solution containing a photoconducllght'sensm'vematenal- The Value of E112 and E115 tive composition for use in theproduction of a photoare Shown the Table 1 below conductive layer wasprepared from the following ingredients: T bl 1 Charge Vpo 1 E Egu'c-ilm-iltll-gyllfflfbflZole 387 mg (2m moles) v g l 'zdicyanomethylene-4H- indenol l.2-b]thiophene 65mg (0.2m mole) :22 HPolyester Adhesive 49000 38 mg (Trade mark of polyester resin sold byEl. Du Pont de Nemours & Co. Inc.)

Similar results are obtained with the corresponding This light-sensitivesolution was applied as a coat on 8-dicyanomethylene-8H compound. analuminium layer on a polyester resin film (thickness: 75 t), using adoctor blade set at a 200 u gap, and then EXAMPLES 2 8 dried in adesicator having silica gel to evaporate a sol- Electrophotographiclight-sensitive materials (No. 2 vent, and further dried at atemperature of 60C for No. 8) of the present invention were obtained byreabout 10 minutes and at a temperature of 120C for 40 peating the sameprocedure as that of Example 1 exabout 2 minutes. A photoconductivelayer having a cept that organic photoconductive compound,sensithickness of about 7 p. was formed on the aluminium tizer,Polyester Adhesive 49000 and tetrahydrofuran layer. were used as shownin the following Table 2 and thick- The sensitivity of theelectrophotographic lightness of photoconductive layer was that as shownin sensitive material (No. l) of the present invention thus Table 2.

Table '2 poly-N-vinyl- 6,8-dinitro- Polyester Tetrathickcarbazole4-dicyanomethyl-' Adhesive h droness ene-4H-indeno 49000 uran of l 1lphoto- No. 2 thiophene conduc- We layer 290 mg 243 mg 46 mg 5.2 g about(l.5 m moles) (0.75 m mole) 12 p. l-bromopyrene formaldehyde do. do. do.do. No. 3 resin 586 mg mg 290 mg 5.3 g about (2 m moles) (0.2 m mole)llu 'do. do. do. do. do. No.4 586mg mg i 324 mg 3.9 g about (2 m moles)(0.4 in mole) llu poly-N-vinyl- 2,6,8-trinitrodo. do. do. carbazole4-dicyanomethyldo. do. do.

ene-4H-indeno No. 5 lthiophene 387 mg 37 mg 37 mg 6.1 g about (2 mmoles) (0.] m mole) 4 u l-bromopyrene do. do. do. do.

formaldehyde about ,u

about 10 y.

about 10 p.

1) Chlorine is contained in a proportion of one chlorine atom permonomeric unit of poly-N-vinyl carbazole.

' 2) Bromine is contained in a proportion of one bromine atom per twomonomeric units of poly-N-vinyl-carbazole.

Vpo, E and E of the light-sensitive materials No. 2 No. 8 were measuredby repeating the same procedure as that of Example 1. The valuesobtained are shown in the Table 3 below.

" Table 3hz,l/32

No. C harge Vpo 112 175 (V) (lux'sec) (lux-sec) in the Examples supra,only 6.8-dinitro-4- dicyanomethy1ene-4H-indeno[ l ,2-b]thiophene(Formula V) and 2,6,8-trinitro-4-dicyanomethy1ene-4H-indeno[1,2-b]thiophene (Formula V1) were used as a sensitizer. However,the values of Vpo, E and E similar to those as shown in the Tables 1 and3 can be obtained by using 4-dicyanomethylene-4H-indeno [1,2-b1thiopheneor its derivatives as shown in Formulas 1 1V in place of theabove-mentioned two 4- dicyanomethy1ene-4H-indeno-[ l ,2-b]thiophenederivatives in amount of from 0.01 to 1 mole per monomeric unit ofpoly-N-vinylcarbazole, chlorinated or brominated poly-N-vinylcarbazole,or l-bromopyrene formaldehyde resin.

Similar results are obtained with the corresponding8-dicyanomethylene-8H compounds with the same compositions.

Electrophotographic light-sensitive materials having sensitivity tovisible light can be produced with an organic photoconductive compoundhaving no sensitivity to visible light by adding 4-dicyanomethy1ene-4H-indeno[l,2-b]thiophene or 8-dicyanomethylene-8H- indeno[2,l-b] thiopheneor their derivatives to said organic photoconductive compounds.

The 4-dicyanomethylene-4H-indeno[ 1,2- b]thiophene compounds of thisinvention are novel.

Such 4-dicyanomethylene-4H-indeno[ l ,2- b]thiophene and its derivativescan be prepared by the process as described below.

R COOR s x (1) Benzoic acid Thiophene ester derivative derivative 1 i X22 00R 2 0t thienylbenzoic ac id ester derivat ive formamide at atemperature of from 50C to C. 7

2 tK-th1enylbenzoic acid derivative the reaction of ring closure asshown above is carried out in the presence of polyphosphoric acid at atemperature of from 70C to 150C. 9

I +HNO3) 2 WM R2 Q Indenothiophenone derivative The nitration as shownabove if it is carried out is effected in the presence of cone. H 80 ata temperature of from 0C to C.

The reaction as shown above is carried out in the presence of piperidinein a solution of tetrahydrofuran.

The novel compounds of formula 6 of the present invention as shown aboveis most useful as a sensitizer for organic photoconductive compoundssuch as poly-N- vinylcarbazole.

The processes of preparing 6,8-dinitro-4- dicyanomethylene-4H-indeno[ 1,2-b]thiophene and 2,- 6,8-trinitro-4-dicyanomethylene-4H-indeno[ 1,2-blthiophene are shown in detail below:

13 g (0.05 mole) of methyl 2-chloro-3,5- dinitrobenzoate (mp 193 196C,Formula 1 as shown above) and 21 g (0.1 mole) of 2-iodothiophene (b.p.71 73C at 16 mm Hg, Formula 2) were dissolved in 100 ml ofdimethylformamide and the solu tion was heated at a temperature of 70C.To this solution was added 20 g of active cupper powder (as prepared bythe method disclosed in Journal of American Chemical Society Vol. Page4219 (1933) by E. C. Kleiderer and R. Adams) over 10 minutes and thesolution was stirred at a temperature of about C for 50 minutes. Afterthe solution has been cooled, the reaction product was poured into 500ml of cold water. The precipitate thus produced was filtered off andwashed with water. After water was removed from the precipitate, theprecipitate was added to 500 ml of acetone. After the stirring has beencontinued, the solution was filtered. The filtrate was treated withactive carbon, and then filtered. The filtrate was condensed to obtain acrude product. 13.1 g of a yellowish crystalline product (m.p. 134 135C)was obtained in an yield by recrystallization of the crude product fromethyl alcohol. This product was identified to be methyl2-athienyl-3,S-dinitrobenzoate (Formula 3) by ultimate red absorptionspectrum at 1730 cm.

23.6 g of methyl 2-a-thienyl-3,S-dinitrobenzoate (Formula 3) thusobtained was dissolved in ml of dioxane and to this solution was addedan aqueous so- 0 lution of NaOH (6 g of NaOH in 200 ml of water) and thestirring was continued for 3 hours. To this solution was added a smallamount of active carbon and the sol-fiicyanomethybnetH-indeno[l,2-b]

thiophene or its derivatives v Found lution was filtered. To thefiltrate was added a cold water and the filtrate was neutralized with6H-HC1 with cooling to obtain a yellowishgcrystalline product. Thecrystalline product was filtered off and washed with water, and thendried. Ayc'rude product (m.p. 171

172C) was obtained in a yield of 21.5 g. A yellowish crystalline product(m.p. 172.5- 173.5C) was obtained by the recrystallization of the crudeproduct from benzene. This product was identified to be 2-athienyl-3,S-dinitrobenzoic acid (Formula 4) by ulti-- mate analysis?Analysis:

C(7r) H(%) N(%) S(%) Calc'ulated for 44.90 2.06 9.52 10.90

' C H N O S The presences of carbonyl group and hydroxyl group wererespectively proved by infrared absorption spectrum at 1,730 cm and3,000 cm".

To 2g of 2-a-thienyl-3,S-dinitrobenzoic acid (Formula 4) was added 60 gof polyphosphoric acid and the mixture was heated at a temperature offrom 130C to 140C. After cooling, the reaction mixture was poured into200 ml of cold water. The precipitate thus produced was filtered off andwashed with an aqueous so- Analysis:

C(7r) H(7() NW1) S(%) Calculated for 47.83 1.46 10.11 11.61

iiH4 2 s Found: 47.65 1.57 10.01 11.62

The presence of carbonyl group was proved by infrared absorptionspectrum at 1730 cm.

1.5 g 6,8-dinitro-4H-indeno[l,2-b]thiophen-4'one (Formula 5) wasdissolved in 30 ml of cone. H SO, and to this solution was addeddrop-wise with stirring, 5 ml of HNO (S.G. 1.38), at atemperature offrom 5C to 10C, over 30 minutes. Stirring was continued at thistemperature for 1.5 hours. This solution was poured into 200 m1 of coldwater. A yellowish crystalline product separated from the solution. Thecrude product was filtered and washed with water and then dried. 1.4 gof a yellowish needle-like crystalline product (m.p. 223 223.5C) wasobtained in an 80.5% yield by the recrystallization of the crude productfrom dioxane-ethyl alcohol. This product was identified to be a novelcompound of 2,6,8-trinitro-4H-indeno[ 1,2-b]thiophen- 4-one (Formula 6)by ultimate analysis.

Analysis:

C( 7z) H('/r) N(%) S(7z) Calculated for 41.16 0.93 13.08 9.98

C 11M 1 Found 40.90 1.32 12.90 10.23

The presence of carbonyl group was proved by infrared absorptionspectrum at 1,730 cm.

8g of 6,8-dinitro-4l-l-indeno[1,2-blthiophen-4-one (Formula 5) and 3.8gof malonitrile were dissolved in ml of tetrahydrofuran and to thissolution was added a few drops of piperidine under reflux. After thereflux was continued to 20 minutes, tetrahydrofuran was distilled off atreduced pressure. The residue was washed with methyl alcohol. 4.4g of6,8-dinitro-4- dicyanornethylene-4H-indeno[1,2-b]thiophene (Formula V;m.p. 244C 245.5C) was obtained by recrystallization of the residue fromdioxane.

Analysis:

C(%) H(%) N(%) S(%) Calculated for 51.85 1.24 17.28 9.89

C H N P,S Found 51.82 1.01 17.62 9.80

The presence of cyano group was proved by infrared absorption spectrumat 2,230".

10g of 2,6,8-trinitro-4H-indeno['1,2-b]thiophen-- 4-one (Formula 6) and4g of malonitrile were dissolved in a mixture of 200 ml oftetrahydrofuran and 200 ml of methyl alcohol and to this solution wasadded a few drops of piperidine under reflux. After the reflux wascontinued for 20 minutes, the crystals separated from the solution werefiltered. After the crystals have been recrystallized from a mixture ofdioxane and acetonitrile, 8g of 2,6,8-trinitro-4-dicyanomethylene-4H-indeno[l,2-b]thiophene (Formula V1; m.p. over 300C) was obtained in theform of red plate crystal.

The presence of cyano group was proved by infrared absorption spectrumat 2,220 cm".

The corresponding S-diCyanomethylene-SH compounds are also novel. Theyare prepared by the reaction of malononitrile on the corresponding81-1,- indeno[2,1-b]thiophene-8-ones as illustrated above. The startingmaterials are prepared by the procedures described in:

MacDowell, et al; J. Org. Chem. 32, 2441 (1967) Dubard, et a1; AcademyScience Ser. C. 271 (4) 311 (1970).

What is claimed is:

1. An electrophotographic light-sensitive material having aphotoconductive layer formed on an electroconductive support, thephotoconductive layer comprising an organic photoconductive monomer oran organic photoconductive polymer, and a sensitizing compound of theformula;

NC -c CN wherein R R R R R and R are hydrogen or nitro groups whereinthe sensitizing compound is present in an amount of from about 0.01 toabout 1.2 mole per mole of the organic photoconductive monomer or permonomeric unit of the organic photoconductive polymer.

2. An electrophotographic light-sensitive material according to claim 1wherein the sensitizing compound is

1. AN ELECTROPHOTOGRAPHIC LIGHT-SENSITIVE MATERIAL HAVING APHOTOCONDUCTIVE LAYER FORMED ON AN ELECTROCONDUCTIVE SUPPORT, THEPHOTOCONDUCTIVE LAYER COMPRISING AN ORGANIC PHOTOCONDUCTIVE MONOMER ORAN ORGANIC PHOTOCONDUCTIVE POLYMER, AND A SENSITIZING COMPOUND OF THEFORMULA:
 2. An electrophotographic light-sensitive material according toclaim 1 wherein the sensitizing compound is6,8-dinitro-4-dicyanomethylene-4H-indeno(1,2-b)thiophene.
 3. Anelectrophotographic light-sensitive material according to claim 1wherein the sensitizing compoUnd is2,6,8-trinitro-4-dicyanomethylene-4H-indeno(1,2-b)-thiophene.
 4. Anelectrophotographic light-sensitive material according to claim 1wherein the sensitizing compound is2,6-dinitro-8-dicyanomethylene-8H-indeno(2,1-b)thiophene.
 5. Anelectrophotographic light-sensitive material according to claim 1wherein the sensitizing compound is2,4,6-trinitro-8-dicyanomethylene-8H-indeno(2,1-b)thiophene.